Present sawing methods generally produce products which do not have consistent quality and growth ring orientation. Present sawing methods produce high degrees of wastage and have difficulty relieving growth stresses similarly in each piece.
Present sawing methods aim to produce a product which is either quartersawn which has the growth rings of the tree basically at right angles to the broad face or backsawn which basically has the growth rings tangential to the broad face.
Present methods for sawing smaller diameter trees with high growth stresses such as species of Eucalyptus generally aim to produce a backsawn product. This involves the cutting of a slab from the side of a log to produce a flat face which would be basically tangential to the growth rings of the tree. This flat face then becomes the "reference" face for further sawing. More sophisticated sawing systems cut two flat faces simultaneously on either side parallel to one another, as shown in FIG. 1A.
Generally further slabs of the desired thickness are cut from the log as at the dotted lines (1) in FIG. 1A. These slabs which are backsawn have the growth stress in the log relieved as bow as at (2) in FIGS. 1B. These slabs are then resawn to the desired width, as in FIG. 3A, as wide boards would be prone be excessive cupping as shown in FIG. 2 as the timber drys. This cupping effect is due to the different shrinkage rates of timber both parallel and at right angles to the growth rings. Timber generally shrinks twice as much parallel to the growth rings as it does at right angles to the growth rings.
A particular slab cut from the log may be wide enough to cut two boards of the desired width but sawing down the middle causes uneven growth ring alignment and stress relieval and causes a combination of spring, as shown in FIG. 3B, and bow and becomes what is generally seen as a low quality piece of timber.
To cut a high quality piece of timber with the stress relieved purely as bow the two edges must be removed as in FIG. 4A. These edges generally go to waste or low value products. The remaining piece of timber has the growth ring alignment of the "perfectly" backsawn piece of timber and will have a degree of bow as shown by (3) in FIG. 4C and will stay "straight" in relation to the broad face if viewed at right angles to the said face as is shown at (4) in FIG. 4B.
A piece of timber of this nature is the aim of backsawn timber production. It is difficult or impossible to produce pieces of timber with this growth ring orientation by conventional means without a high degree of wastage.